1. Field of the Invention
This invention pertains to the field of cellular polyurethane elastomers. In particular it pertains to such elastomers having relatively high densities and superior thermal, mechanical and physical properties.
2. Description of the Prior Art
The preparation of cellular polyurethane elastomers by reacting higher molecular weight polyhydroxyl compounds such as polyesters or polyethers with organic diisocyanates into isocyanate-group containing prepolymers and the subsequent reaction with water to which auxiliaries may optionally be added is described in the Plastics Handbook, Vol VII, "Polyurethanes" by R. Vieweg and A. Hoechtlen, Carl Hanser Publishers, Munich 1966, pages 275-287 and 330-337.
According to a procedure in German Published Application 29 20 502, an isocyanate-containing prepolymer is reacted with higher molecular weight polyhydroxyl compounds, 0.3 to 1 percent by weight of water, 0.1 to 0.8 percent by weight of aromatic primary diamine with a molecular weight of 108 to 500, with the percent by weight in each case being based on the overall reaction mixture, and, optionally, glycols with a molecular weight of 62 to 250, in order to prepare the cellular polyurethane elastomers. Employing this procedure, products with relatively high densities can be produced without encountering excessive gas pressure during foaming.
Cellular polyurethane elastomers differ from polyurethane foams by their considerably higher densities which vary in the range of 100 to 800 grams per liter and their better physical properties which permit their use in applications not open to ordinarly lower density foams. They are therefore used for resiliency and absorption elements in vehicle and machine construction, for buffers, gaskets, shoe soles and similar purposes.
Because of the often extreme strain, primarily thermal and mechanical, under intended use conditions, generally high-performance polyurethane systems are required for cellular polyurethane elastomers. This results in several derived problems based on prior art. The systems based on 1,5-naphthalene diisocyanate, for example, result in elastomers with good properties but are very expensive. Those based on 3,3'-dichloro-4,4'-diamino diphenylmethane use are extremely dangerous physiologically and can therefore be made only with extreme precautionary measures. 4,4'-Diisocyanatodiphenylmethane, on the other hand, while safe to use and relatively inexpensive, results in cellular polyurethane elastomers which usually cannot meet the extreme mechanical requirements.